Wireless Local Area Network (WLAN) technology has significantly matured over the last decade and while it continues to function well, there are scenarios where it struggles to deliver acceptable performance for the most basic services. Due to the success of WLAN, wireless networks are increasingly getting denser in order to meet huge traffic demand. It has been challenging for current wireless networks to tackle some problems due to the high density, notably, the overlapping basic service set (OBSS) problem.
Generally, wireless networks comprise a wireless access point (AP) which allows wireless stations (STAs) to wirelessly connect to a wired network. A wireless station is a device which has the capability to connect wirelessly to a wireless network, for instance, via the 802.11 wireless protocol. A wireless access point (AP) has station functionality but also manages all the distributed stations within a network and is able to connect to a wired network to provide the stations within the wireless network with access to the wired network.
One of the main causes of wireless performance deterioration is overcrowding of devices in the unlicensed bands where WLANs typically operate. This is particularly a risk in dense deployment environments, such as apartments, conference venues and shopping centres.
Increased density increases the likelihood of collision between two wireless transmissions, unless steps are taken to mitigate this likelihood.
One approach to attempt to reduce the possibility of collision is for a station (STA), before using a channel, to sense the channel to determine if the channel is clear to be used. This is often governed by clear channel assessment (CCA) thresholds, parameters used to define the sensitivity of a station to incoming transmission from other STAs. If signals are received that have a received signal strength that is below the CCA thresholds, then the signals are ignored and the station is free to transmit over the channel. Accordingly, the higher the CCA thresholds, the less sensitive the device is to wireless signals.
An alternative method of preventing clashes between nearby networks assigns a different “colour” to each network. A single network is a single basic service set (BSS), comprising at least one access point and one station. Each BSS is assigned a colour which is communicated to the stations in the BSS. When a station or access point in the network transmits, it includes an indicator of the colour of the network. When a station or access point (the receiving device) receives this information, it checks whether the colour indicated in the received data is the same as the colour for the network in which the receiving device is operating. If the colour is different, the received signal is ignored if the received signal strength is below a predefined deferral level. This allows stations and access points to ignore signals from devices outside of their network.
Dynamic Sensitivity Control (DSC) is a method in which one or more of the CCA thresholds for a station are varied to minimise overhearing other devices operating on the same channel in adjacent networks (crosstalk). This is relatively straightforward from the perspective of non-access point, station nodes because the stations merely need to ensure that the adapted CCA thresholds still enable them to hear the access point. The situation is more complicated on the access point side as the access point has to track multiple stations and ensure that it does not disconnect any stations by increasing the CCA thresholds (and thereby reducing the sensitivity) too far.
Problems may arise where existing nodes connected to the access point may move away from the access point thereby going out of range of the access point. Similarly, new nodes that wish to associate with the access point may arrive but are prevented from accessing the network because of the access point's curtailed CCA range. In such scenarios it is desirable that there exists a way to detect such problems and trigger the DSC algorithm to relax the CCA thresholds to increase the range of the access point and mitigate any problems associated with coverage holes.